Skip to main content

Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

See other formats

a half century or thereabouts. Sometimes as much as 25 feet outside the area where trees were being overwhelmed, shrubs were crushed and trees barked and broken by blocks of ice that had tumbled from the glacier margin.
The south side of Bryn Mawr Glacier showed active advance at the time of our visit, the margin of the glacier having a push moraine made up of gravel on the beach and alluvial fan, and of turf and soil farther back from the shore. The site of a push moraine of 1899 was completely overridden and the new push moraine, 6 to 10 feet high,was filled with trunks of overwhelmed shrubs, many of them still retaining the leaves of 1910 growth. In some places the turf outside of the push moraine had been shoved up into low arches by the advancing glacier. Willows and alders that were being overwhelmed were from 10 to 15 years old, and in one case possibly as much as 25 years old. There was no barren zone left on the south side of the glacier, the advance having entirely covered it.
This advance had displaced the south marginal stream so that it was Sowing through the bushes south of its previous course and carrying them down-stream. At one point a lobe of the ice which was swept by the stream had been undercut until a small avalanche of ice blocks was formed and these blocks were floating down the stream toward the sea, coming from a point on the glacier margin nearly a quarter of a mile from the fiord. Near the beach the drainage was obstructed by the ice advance and several small pools were formed between the advancing ice front and an older terminal moraine. At several points along this southern margin of Bryn Mawr Glacier the upper layers of the ice had been thrust-faulted forward over the lower layers so that splinters of ice projected into the forest, as was the case on a larger scale at Columbia Glacier.
The area on the southern border of Bryn Mawr Glacier which is being overridden, is part of a crescentic terminal moraine, with knobs and basins, built by the glacier at a time of much greater expansion, and now grassed over and partly covered by alders and spruces, some 65 years old. It is, therefore, at least that long since this older terminal moraine was built.
Vassar Glacier. Vassar Glacier differs from Smith and Bryn Mawr in having a well-defined bulb at the lower end. The glacier heads in cirques 4000 to 5000 feet above sea level, and is about $ miles long, a mile wide at its snowfield, and three-eighths of a mile wide where it plunges over the lip of its hanging valley at a level of 1598 feet, above which is a second cascade at a level of a little more than 200 feet. After cascading down the hanging valley lip to the fiord level, with a slope of 2500 feet to the mile, the glacier extends eastward a half mile further with a much flatter grade and with a lobate lateral expansion. This glacier with its three portions, a moderately-sloping upper part, a cascading middle section, and a flattened terminus, reminds one of the Rhone Glacier in the Alps, except that it terminates hi the sea, while the Rhone Glacier ends in a valley on the land. As already stated, a minor lobe of the Vassar Glacier terminates 2000 feet above the fiord and sends a stream down the fiord wall.
Vassar Glacier has no lateral moraine on the south side, but there is a weak one on the north, and one medial moraine, starting below the lip of the hanging valley, but not from a lateral moraine, as there are no noteworthy tributaries. The whole of the lobate lower portion, however, is mantled with thick ablation moraine, which extends up the southern margin of the cascading portion to a height of 1100 feet, but on the northern margin ends at an elevation of about 300 feet. In contrast with the other